Determining the exact location of a receiver in an environment can be quite challenging, especially when the receiver is located within a building. Imprecise estimates of the receiver's position may have “life or death” consequences for the user. For example, an imprecise estimated position of a mobile phone operated by a user calling 911 can delay emergency personnel response times. In less dire situations, imprecise estimates of the user's position can negatively impact efforts to provide navigation to a desired destination or status updates regarding the user's location.
Estimates of a receiver's latitude and longitude can be computed using known techniques, and later used to identify a building in which the receiver is located. An estimate of a receiver's altitude can also be computed using known techniques, and later used to identify a floor of that building at which the receiver is located. One known approach for estimating the altitude of a receiver relates pressure measured by the receiver with pressure at a known height. Unfortunately, the pressure measured at the position of the receiver inside the building may not be the same as the ambient pressure at the same altitude outside the building. Such pressure discrepancies are due to the stack effect and building pressurization from heating, ventilation and air-conditioning (HVAC) systems. These pressure discrepancies may change over the course of seasons as the HVAC system heats or cools the building. These pressure discrepancies result in estimates of altitude that deviate from the actual altitude of the receiver. In order to accurately map the receiver's altitude to a floor of a building, the precision of the receiver's estimated altitude must be within an acceptable vertical range. For instance, in a building that has a 3 meter separation between each floor, a deviation of 3 meters from the receiver's true altitude could send emergency responders to the wrong floor. Thus, solutions are needed to identify and correct for indoor pressure discrepancies in order to estimate altitudes with desired accuracy.